In recent years, development has progressed to decrease the thickness and weight of laptop personal computers. Along with the above, a decrease in thickness has increasingly been demanded for polarizers employed in liquid crystal display devices. Specifically, in order to decrease the thickness of polarizers, a decrease in thickness of a polarizer protective film has increasingly been sought. However, it has become clear that when only the thickness of polarizing plate protective films is decreased, various drawbacks result.
As one of them, polarizers are adversely affected by moisture permeability (being moisture transmittance). For example, along with a decrease in thickness of the polarizer protective film, moisture transmittance increases. As a result, durability of the polarizer is degraded. In order to improve the above moisture transmittance, various methods are proposed. It is assured that as the moisture transmittance decreases, durability of the resulting polarizer is enhanced. On the other hand, a drawback has been found in which during adhesion of a polarizer protective film to a polarizer, adhesive agents are not sufficiently dried due to its low moisture permeability.
Therefore, a polarizer protective film is required to exhibit targeted moisture permeation characteristics to satisfy both. Specifically, the moisture transmittance of the polarizer protective films, incorporating cellulose ester, which are now commonly employed, is markedly increased due to a decrease in film thickness.
In view of the foregoing, developments of a cellulose ester film which is provided with physical properties such as desired moisture permeability and high dimensional stability and a polarizer protective film using the same are highly sought. For example, a technology is disclosed in which moisture transmittance is lowered by the addition of plasticizers into a cellulose ester dope (refer, for example, to Patent Document 1). However, with only the addition of plasticizers, it is difficult to realize the targeted moisture transmittance. Further, a technology is disclosed in which a resin layer is provided on a cellulose ester film (refer, for example, to Patent Document 2). However, in order to achieve high water vapor barring performance, a relatively thick film is typically needed and its application to a polarizer protective film is not preferred.    Patent Document 1: Japanese Patent Publication Open to Public Inspection (hereinafter referred to as JP-A) No. 2003-221465    Patent Document 2: JP-A No. 2002-301788